Coexistence of polar and nonpolar domains and their photocontrol in the B7 phase of a bent-core liquid crystal containing azo dyes.

Coexisting polar and nonpolar domains have been studied by means of texture observation, x-ray analysis, optical second-harmonic generation (SHG), and SHG microscopy in the B7 phase of a bent-core mesogen doped with azo dyes. The bent-core molecules take a planar orientation and show high birefringence in the polar domain, while they take a homeotropic orientation and show low birefringence in the nonpolar domain. Good correspondence between real and SHG images was observed under a SHG microscope; the bright (high-birefringent) domain is SHG active and the dark (low-birefringent) domain is not SHG active. Photoisomerization of the azo dyes causes layer reorientation from the layer perpendicular to the substrate to that parallel to it.